For some medical disorders, brain stimulation has been a primary treatment alternative to pharmacotherapy, and electroconvulsive therapy (ECT, or “electroshock” therapy) has been the dominant brain stimulation approach since the first part of the 20th century. ECT carries risks of memory and other cognitive side effects, considerable cost, and risks of anesthesia. Two implantable approaches have also been described: deep brain stimulation (DBS), in which electrodes are implanted directly within the brain, and vagus nerve stimulation (VNS) in which stimulating electrodes are implanted on the vagus nerve in the neck. While the U.S. Food and Drug Administration (FDA) have approved systems for deep brain stimulation for the treatment of Parkinson's disease, DBS is presently an experimental intervention for other neuropsychiatric conditions. The risks of DBS include infection, hemorrhage, and injury to deep brain structures. In reports of clinical studies with VNS, many of the patients who undergo VNS treatments do not achieve remission, and there is no reliable predictor of good outcomes from the implanted VNS device.
A far safer and less invasive implantation approach has been developed by for the stimulation of the trigeminal nerves. For example, the ophthalmic nerves ascend from foramen above the eyes and ascend toward the hairline. These nerves are relatively superficial in that the plate-like portion of the skull (the squama frontalis) that defines the forehead is itself quite superficial with regard to the forehead skin surface. There is thus a relatively thin portion of subcutaneous tissue, fascia, and muscle between the forehead skin surface and the underlying bone.
In its least invasive form, a cutaneous electrode is applied to the forehead to stimulate the ophthalmic nerves. Such an application is quite advantageous in that a lay person can readily center an appropriate “bandaid” electrode on their forehead adjacent or above their eyebrows. Thus, a lay person can readily position the cutaneous electrode without requiring any specialized knowledge or training. Moreover, the superficial depth of the ophthalmic nerves on the forehead means that the nerves are readily stimulated by current levels that are easily tolerated by patients. The amount of current may thus be regulated so that the brain itself is never subjected to any current (or subjected to such vanishingly small amounts of current that the currents have no deleterious effects). In contrast, it was conventional to propose the implantation of electrodes on the trigeminal nucleus. This invasive implantation is fraught with dangers of meningitis and nerve damage. But even if it were done safely, the resulting excitation is so close to the brain that the brain is then exposed to harmful amounts of current. In contrast, a cutaneous electrode application to the forehead involves none of the risks involved with the conventional invasive approaches and also isolates the brain from exposure to electrical current. What is even more remarkable is that the cutaneous stimulation of the ophthalmic has proven to be more clinically efficacious than conventional invasive approaches such as implantation on the vagus nerve for treatment of disorders such as epilepsy.
The cutaneous electrodes typically need only be applied at night before a patient sleeps. The electrodes can then be removed upon waking so that a patient can resume a normal routine during the daytime hours. Although a cutaneous stimulation of the ophthalmic nerves is thus not only safer but more efficacious than conventional treatments, the electrodes must be worn during the therapy—they cannot stimulate the ophthalmic nerves at a distance. There may be certain patients who cannot tolerate the nightly application of the electrodes. Moreover, it may be the case that the neurostimulation therapy needs to be applied throughout the day as well. A patient would naturally be reluctant to be out in the public even with flesh-colored electrodes on their forehead. For such patients, subcutaneous neurostimulation therapies are indicated. In that regard, a subcutaneous electrode by definition may be placed closer to a targeted nerve or in actual contact with a targeted nerve as opposed to an overlying cutaneous electrode. So a subcutaneous approach has the advantage of a more direct stimulation of the targeted nerve and enables the use of less current as well.
Accordingly, there is a need in the art for cutaneous electrodes for neurostimulation of nerves such as the ophthalmic nerves and corresponding implantation techniques.